Conventionally, an electricity storage module is known that has a housing accommodating a plurality of battery cells such as lithium ion batteries and supports the battery cells by sandwiching them from both sides by means of a pair of side plates that constitute the housing (PTL 1). Through holes are provided in the side plates correspondingly to respective ones of the plurality of battery cells and each through hole is closed by an electrode terminal surface of the battery cell. The battery cell is, in both ends thereof, engaged into through holes of the pair of the side plates so that the position of the battery cell is constrained. An electrically conductive member is welded on the electrode terminal surface of the battery cell which is positioned by the side plates.
The material of the side plates that constrains the position of the battery cell is polybutylene terephthalate (PBT), while the material of the electrically conductive member that electrically connects the battery cells is copper. That is, the materials for both components are different from each other. The coefficient of linear expansion of PBT is in the order of 6.0×10−5 [1/K], while the coefficient of linear expansion of copper is in the order of 1.7×10−5 [1/K]. Therefore, if the temperature of the electricity storage module increases and the side plate is thermally expanded, the distance between the battery cells increases. Although the electrically conductive member also thermally expands with an increase in temperature of the electricity storage module, a difference in thermal expansion occurs since the coefficient of linear expansion of copper is smaller than the coefficient of linear expansion of PBT. As a result, the stress due to thermal change is generated at a welding part between the electrically conductive member and the electrode terminal of the battery cell.
In the electricity storage module according to PTL1, the side plates that constrain the position of the battery cell are coupled to an inlet flow path forming plate, an outlet flow path forming plate, an inlet side guiding plate, and an outlet side guiding plate made of rigid metal plates, by means of fastening means such as screws. If the above-described flow path forming plates and guiding plates are made of aluminum diecast or the like having a coefficient of linear expansion of the order of 2.1×10−5 [1/K], for example, deformation due to thermal change in the side plates is suppressed by the above-described flow path forming plates or guiding plates.